Extensions of previous work and new projects are proposed in the following areas: 1) Studies on the isolation and in vitro translation of proinsulin messenger RNA and the characterization of preproinsulin, the in vitro translation product of this messenger RNA. 2) Preparation of cDNA molecules using purified insulin mRNA as primers. 3) Continued studies on insulins and proinsulins from various species and on the subcellular organization of the insulin biosynthetic machinery of the beta cell. 4) Isolation and characterization of beta cell plasma membranes, and studies on antigenic components of the membranes. 5) Tissue culture studies with normal islets and inducted beta cell tumors in rats and mice.